Balloon catheters are commonly used for carrying out a procedure or an investigation at a remote location in a human or animal subject. For example, such balloon catheters are used for determining the volume of a stomach, or a part thereof subsequent to bariatric surgery. Such balloon catheters are also used for determining the transverse cross-sectional area at locations within the stomach, or of a sphincter, for example, an oesophageal sphincter. Additionally, such balloon catheters are used for determining the transverse cross-sectional area of a vessel or lumen, for example, the oesophagus, and in particular, a diseased portion of the oesophagus which may have resulted in an occlusion. Additionally, such balloon catheters are used for dilating an occlusion in a vessel or lumen, for example, for dilating an occlusion in the oesophagus resulting from a diseased portion of the oesophagus. Such balloon catheters are also used for ablating diseased tissue in a lumen or vessel, such as the oesophagus. Such balloon catheters are also used for determining the volume and/or transverse cross-sectional area of vessels and lumens.
Similarly, such balloon catheters are used for carrying out procedures and investigations in the cardiovascular system, for example, for determining the volume and/or transverse cross-sectional area of a vessel of the cardiovascular system, and are also used for dilating an occlusion in a vessel of the cardiovascular system, as well as for stent placement and ablating tissue in a vessel of the cardiovascular system.
Such balloon catheters comprise an elongated catheter extending between a proximal end and a distal end, and an inflatable element, namely, a balloon located on the catheter, which typically, is located towards the distal end of the catheter. The catheter extends through the balloon so that the balloon defines with the catheter an annular hollow interior region. Typically, a lumen extends through the catheter from the proximal end thereof to the balloon which communicates with the hollow interior region of the balloon for inflating the balloon. Inflating and deflating of the balloon is carried out by delivering and withdrawing, typically, a liquid inflating medium into the balloon through the inflating lumen. In order to facilitate determining the volume or the transverse cross-sectional area of a vessel or lumen within which the balloon is located, at least one, and typically a pair of stimulating electrodes are provided within the balloon on the catheter axially spaced apart from each other, and a plurality of axially spaced apart sensing electrodes are provided within the balloon on the catheter between and axially spaced apart from the stimulating electrodes. A plurality of mutually insulating wires extend through a wire accommodating lumen which extends from the proximal end to the balloon so that the wires can be individually coupled to corresponding ones of the stimulating and sensing electrodes. When the balloon is inflated with an electrically conductive inflating medium, which typically is a liquid saline solution, by applying a stimulating electrical current of known constant value to the stimulating electrodes, voltages produced on the sensing electrodes are indicative of the transverse cross-sectional area of the balloon adjacent the respective sensing electrodes. Accordingly, by reading the voltages produced on the sensing electrodes, the transverse cross-sectional area of the balloon adjacent the sensing electrodes can be computed, and in turn the volume of the balloon can be computed. Thus, by inflating the balloon to fill the vessel or lumen, the volume and the transverse cross-sectional area of the vessel or lumen at locations adjacent the sensing electrodes can be computed by reading the voltages produced on the sensing electrodes resulting from the constant current signal applied to the stimulating electrodes.
Such balloon catheters will be known to those skilled in the art.
However, a problem with such balloon catheters is that it is difficult to determine when precisely the balloon has been inflated so that the balloon just fills the vessel or lumen the volume or the transverse cross-sectional area of which is to be determined without dilating the vessel or lumen. In general, in order to determine when the balloon has been inflated to just fill the vessel or lumen, the pressure of the inflating medium is monitored. This, typically, requires the provision of a pressure sensor at the proximal end of the catheter of the balloon catheter, which monitors the pressure of the inflating medium adjacent the proximal end of the catheter. Inflating of balloon catheters is normally carried out by pumping the inflating medium, which, in general, is a liquid, such as an electrically conductive saline solution, into the balloon through the inflating lumen from a syringe containing the inflating medium. Alternatively, the inflating medium may be pumped from a reservoir by a suitable pump. Prior to inflating the balloon, both the balloon and the inflating lumen contain air. Thus, where the inflating medium is a liquid inflating medium, after inflating of the balloon with the liquid inflating medium, the inflating medium in the balloon and in the inflating lumen of the balloon catheter will include air. The presence of air in the liquid inflating medium in both the balloon and in particular, in the inflating lumen of the balloon catheter renders it virtually impossible to obtain a true pressure reading of the pressure of the liquid inflating medium in the balloon. The air in the liquid inflating medium forms an air pocket in the inflating lumen, which results effectively in an open hydraulic circuit between the balloon and the proximal end of the catheter. Accordingly, the presence of such an air pocket in the inflating lumen acts to prevent the pressure sensor at the proximal end of the catheter producing a true reading of the pressure of the liquid inflating medium in the balloon.